Stemming Plug

ABSTRACT

The invention relates to a stemming plug ( 10 ) which is made from a suitably resilient plastic material and comprises two cup-shaped members ( 12,14 ) which face each other with their rims ( 22 ) in abutment and means, which extends between the centres of the base portions of the cups ( 20 ) in the plug ( 10 ), which is adapted to move the bases of the cups ( 20 ) towards each other to compress the cups ( 10 ) and cause a circumferential zone of the plug ( 10 ) on either side of the abutting faces of the cups ( 20 ) to increase in radial dimension to be brought into load bearing contact with the side of a predrilled hole ( 38 ) in which the plug ( 10 ) is to be located, in use, and to enable the bases of the cups ( 20 ) to be moved away from each other to allow the plug ( 10 ) to be withdrawn from the hole ( 38 ) in the event of a misfire of the explosive in the hole ( 38 ).

FIELD OF THE INVENTION

This invention relates to a stemming plug for confining explosive blastgasses in a blast hole in mining, tunneling or like operations.

BACKGROUND TO THE INVENTION

A variety of stemming plugs are produced from natural rubber, syntheticrubber and other suitable polymers and have been used for the aboveapplication for many years. An unacceptably high degree of failure is,however, experienced by miners and the like as a result of the stemmingplugs being expelled from blast holes during a blast. Difficulty ininserting existing plugs into holes and, when occasion requires, theremoval of a plug are problems frequently encountered in blastingoperations.

SUMMARY OF THE INVENTION

A stemming plug which is made from a suitable resiliently deformableplastics material according to the invention comprises two cup-shapedmembers which face each other with their rims in abutment and means,which extends between the centres of the base portions of the cups inthe plug, which is adapted to move the bases of the cups towards eachother to compress the cups and cause a circumferential zone of the plugon either side of the abutting faces of the cups to increase in radialdimension to be brought into load bearing contact with the side of apredrilled hole in which the plug is to be located, in use, and toenable the bases of the cups to be moved away from each other to allowthe plug to be withdrawn from the hole in the event of a misfire of theexplosive in the hole.

A portion of the wall of each cup-shaped member from its rim may besubstantially cylindrical around the axis of the plug which passesthrough the centres of the cup bases to define the circumferential loadbearing zone of the plug.

Each cup-shaped member may include a substantially cylindrical skirtwhich extends from the substantially cylindrical portion of its wallaway from the abutting rims of the cups to surround at least a portionof the cup wall.

The composite substantially cylindrical outer wall of the plug may bedivided into segments by slots which are parallel to the plug axis.

The outer surface of each of the wall segments could include outwardlyprojecting formations for gripping the surface of a hole when thesegments are brought into load bearing contact with the surface, in use.

The gripping formations may be ribs which are parallel to the segmentdefining slots.

The non-cylindrical wall material of each cup-shaped member may includea line of weakness on the inside of and against the wall of the cupacross each of the wall segment slots. The line of weakness may bedefined by arcuate slots with the ends of each slot being spaced fromthe ends of adjacent slots.

The non-cylindrical portion of each of the cup-shaped members mayinclude a pleat which extends from the ends of each of the arcuate slotsin a direction towards the plug axis to expedite expansion of the plugin a radial direction, in use. The pleated wall material of eachcup-shaped member is preferably thinner than the adjacent cup wallmaterial.

The pleats may be V or C-shaped in cross-section.

The non-cylindrical portion of each of the cup-shaped members mayinclude an aperture through which a fuse or electrical detonatorconductors may be passed.

Each of the cup-shaped members preferably includes a formation which isreleasably engageable with a formation on the other cup to ensure thatthe fuse apertures are in register with each other and to preventrotation of the cups relatively to each other about the plug axis.

The releasably engageable formations may be a plurality ofcircumferentially spaced sockets and spigots which are releasablyengageable with the sockets and spigots of the other cup.

A first of the cup-shaped members may include a holed boss in its baseand the second an aperture in its base and the cup base moving meanscould be a headed elongated element which passes axially through theplug cavity between the first and second cups with its head, which isadapted for rotation by a removable tool, bearing on the outer surfaceof the second cup around the aperture with a portion of its length fromits unheaded end including formations which are movably engageable withcomplementally shaped formations in the hole in the boss of the firstcup member. The engageable formations on the end portion of theelongated element and in the boss hole may be helical thread formations.

In a variation of the above stemming plug a first of the cup-shapedmembers may include an aperture in its base around the plug axis, atleast two outwardly projecting gripper formations which are attached toand project outwardly from the base of the cup to be biased towards theplug axis over the aperture and carry on their faces which face the plugaxis ratchet teeth, the second cup-shaped member may carry an elongatedelement which passes through the aperture in the first cup and betweenthe gripper formations and carries ratchet teeth which are oppositelydirected to those on the faces of the gripper formations with thedirections of the ratchet teeth being such that the end of the elongatedelement may be pulled outwardly from between the teeth of the gripperformations to draw the cup bases towards each other to set the plug, inuse, when the pulling tension on the elongated element is relaxed. Theplug could include two gripper formations which face each other fromopposite sides of the aperture in the base of the cup and the portion ofthe elongated element which carries its ratchet teeth may be square orrectangular in cross-section with the ratchet teeth on two oppositesides of the element while the remaining opposite sides are flat so thatthe ratchet teeth on the gripper formations will, when the elongatedelement and the cup to which it is attached is rotated through 90°, bedisengaged from the ratchet teeth on the elongated element to enable thebase portions of the cup-shaped elements of the plug to move away fromeach other to reduce the radial dimension of the plug to enable it to beremoved from a predrilled hole in the event of a misfire of theexplosive in the hole.

Each of the gripper formations could include at its free end a surfacewhich tapers from the end of the formation inwardly towards the plugaxis for releasing its ratchet teeth from those on the elongated elementby means of a suitable tool.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of embodiments of the invention are now described by way ofnon-limiting examples only with reference to the drawings in which:

FIG. 1 is a half-sectioned side elevation of a first embodiment of thestemming plug of the invention,

FIG. 2 is a plan view of the cup-shaped members of the FIG. 1 stemmingplug,

FIG. 3 is a sectioned side elevation of the FIG. 1 stemming plug, inuse,

FIG. 4 is an isometric view of a tool for setting the FIG. 1 stemmingplug,

FIG. 5 is sectioned side elevation of a variation of the FIG. 1 plug,

FIG. 6 is a sectioned side elevation of a second embodiment of acup-shaped formation of the stemming plug of the invention,

FIG. 7 is a plan view of the FIG. 6 cup-shaped member,

FIG. 8 shows two fragmentary sectional views which illustrate thefunction of the pleats in the cup-shaped member of FIGS. 6 and 7,

FIG. 9 is a sectioned side elevation of a typical cup-shaped member ofthe stemming plug,

FIG. 10 is an under plan of the cup-shaped member of FIG. 9,

FIG. 11 is an under plan of the second cup-shaped member for use withthat of FIG. 9, and

FIG. 12 is a sectioned side elevation of a third embodiment of thestemming plug of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The first embodiment 10 of the stemming plug of the invention is shownin FIG. 1 to include two cup-shaped members 12 and 14 with their rimsabutting each other and a headed setting screw 16.

The cup-shaped members 12 and 14 are made from a suitable resilientplastic material such as polypropylene, a polyamide or the like. Thescrew 16 is made from a suitably rigid polyamide.

The upper cup-shaped member 18 in FIGS. 1 and 2 is shown to include anoutwardly domed wall portion 20 with the rim portion 22 of the cup beinginwardly directed to be almost cylindrical about the axis of the plug.The cylindrical portion 22 of each cup side wall is extended away fromthe portion 22 to provide cylindrical extensions 28 which surround thedomed wall portions 20 and bases of the cups.

The base portion of the cup 20 carries a boss 24 which has a threadedbore which is engaged by the male helical thread formation on the screw16.

The cup-shaped formation 14 is substantially identical to the cup 12save that it carries in its base portion a holed recess formation 26 foraccommodating and locating the head of the screw 16.

As shown on the left in FIG. 1 and in FIG. 2 the cylindrical portions 22of the cup-shaped members 12 and 14 together with their cylindricalextensions 28 provide a substantially cylindrical composite wall whichsurround the remainder of the cups.

The composite stemming plug wall is shown in FIGS. 1 and 2 to be dividedinto segments 30 by vertical slots 32 which penetrate the domed portion20 of the plug to allow for movement of the segments away from the plugaxis and one another, in use. The outer surfaces of each of the wallsegments 30 carry an outwardly projecting rib 34 the purpose of which isto be deformed under radial pressure against a wall of a hole in whichthe plug 10 is located, in use, to key into irregularities in the wallsurface and so to prevent rotation of the plug as it is being set in thehole. The dome portion 20 of each of the plugs carries an aperture 36,shown only in FIG. 2, for the passage of a fuse or the conductor leadsto an electrically activated detonator.

FIG. 3 illustrates the stemming plug 10 of FIGS. 1 and 2 set in apredrilled blast hole 38 with its cup-shaped members compressed towardseach other by the screw 16 with at least the radially so-moved wallportions 22 of the cup segments 30 pressed hard up against the surface40 of the hole 38.

The stemming plug 10 is set in the hole 40 by means of the tubular tool42 shown in FIG. 4. The tool includes, from one end, two opposedvertical slots 44 which terminate in round ended circumferential slots46. The diameter of the bore of the tool 42 is slightly greater than thediameter of the outer portion of the screw 16 head and the width of theslots 44 and 46 are similarly slightly larger than the diameter of thetrunnion formations 48 which project from opposite sides of the screwhead. The tool additionally carries a handle, at its opposite end tothat at which the slots 44 and 46 are located, by means of which thetool is rotated in setting the stemming plug.

The FIG. 5 variation 50 of the stemming plug of the invention is similarto that of FIGS. 1 to 3 except that the domed wall portions 20 of theFIG. 1 plug is here replaced by frusto conical wall portions 52 and theboss 24 is replaced by a recessed formation 26, which is identical tothe screw head recess formation 26 of FIG. 1. The upper formation 26 inFIG. 5 carries a threaded plug 54 in which the screw 16 is engaged. Theplug carries a key, not shown, which is engageable with a key groove inthe recess 26 to prevent rotation of the plug 54 during setting of thestemming plug.

The composite cylindrical wall of the FIG. 5 stemming plug includesslots 32, ribs 34 and the fuse aperture 36 in its wall portions 52 whichare identical to those described with reference to FIGS. 1 and 2.

The second embodiment 56 of the stemming plug of the invention is shownin FIGS. 6 and 7 to include six pleats 58 which are located in the domedor frusto conical wall portions of the cup-shaped members and extendacross the segment 30 wall slots 32 as shown in FIG. 7. The outer edgesof the pleats 58 terminate in arcuate slots 60 which are made throughthe cup material to separate the outer wider edges of the pleats 58 fromthe wall segments 30.

The pleats 58 in this embodiment of the invention are outwardlyV-shaped, as most clearly shown in FIGS. 7 and 8. The upper sketch inFIG. 8 shows the shape of the edge of the pleat at its slot 60 in theunstressed condition of the stemming plug and the lower sketchillustrates the degree of stretch provided, by the six almost flattenedpleats, to enable the cup segments to separate circumferentially whenthe stemming plug is stressed and set as illustrated in FIG. 3. Thepleats need not necessarily have the V-shape shown in FIGS. 7 and 8 andcould be C-shaped or have any suitable stretchable shape such as aplurality of tapered corrugations or the like. Whatever thecross-sectional shape of the pleats is the material of the pleats ismade to be thinner than the remaining domed or frusto conical cupmaterial adjacent them.

The pleats, and particularly those which are composed of a thinnermaterial, facilitate outward radial and circumferential expansion of thesegmented plug wall and markedly reduce the torque which is required torotate the screw during setting of the stemming device.

FIGS. 9, 10 and 11 illustrate the currently preferred arrangement forpreventing rotation of the stemming plug cup-shaped members relativelyto each other during setting of the stemming plug. An arrangement ofthis sort is applicable to all of the stemming plug embodimentsdescribed in this specification.

The cup-shaped member of FIGS. 9 and 10 is shown to include two spigotformations 62 and four sockets 64 which are supported by and inprotuberances 66 which project from the centres of the wall segments 30.The lower ends of the protuberances 66 are flush with the outer surfacesof the rims of the cup shaped members. The plan view of the oppositecup-shaped member of the stemming plug is shown in FIG. 11 to includetwo spigots 62 on either side of the fuse or electrical cord aperture 36and four sockets 64.

The sockets 62 and the spigot 64 of the two cup-shaped members areengaged with each other in the assembled stemming plug.

The arrangement of the sockets 64 and spigots 62 on the rim faces ofeach of the cup-shaped members is firstly to ensure that the two cupsare connected in a specific circumferential relationship so that thefuse holes 36 will always be in axial register for the passage of a fuseor detonator conductors through the plug and, secondly, to hold theabutting cup faces together to avoid one segment face portion from beingradially displaced from the other as the cups are activated bycompression towards each other or by wall irregularities in the blasthole.

The third embodiment 68 of the stemming plug of this invention is shownin FIG. 12 to include cup-shaped members 70 and 72, an actuator 74 andtwo gripper formations 76.

The substantially cylindrical wall of the stemming plug is the samesegmented arrangement as that of FIG. 1.

The actuator 74 is made integral with and projects from the base of thecup 72. The portion of the length of the actuator which carries ratchetteeth 78 is rectangular in cross-section with its non-toothed sidesbeing smooth. The two gripper formations 76, without the actuatorbetween them, are strongly biased by the resilience of the material fromwhich they are made, over the aperture in the plug towards the plugaxis. Each of the gripper formations 76 carries, when the actuator islocated between them, ratchet teeth which are biased into engagementwith the teeth 78 on the actuator. The tooth direction of the engagedratchet teeth, as shown in the drawing, enable the actuator to be pulledupwardly in the drawing from between the actuator ratchet teeth tocompress the cup-shaped members, as does the screw of FIG. 1, to movethe wall segments into pressure bearing contact with a hole wall, inuse. When the plug is set in a hole the outward tension on the actuatoris relaxed to allow the ratchet teeth to lock the plug in its activatedstate in the hole.

To release the holding tension on the actuator to enable the plug to beremoved from the hole, after use, a tool having opposite triangularformations is pressed into the triangular gaps between the upper ends ofthe gripper formations 76. Pressure on the tool forces the gripper teethout of engagement with the actuator teeth to allow the tension on theactuator to draw the actuator back into the plug cavity and so releasethe wall segments from the hole wall.

The invention is not limited to the precise details as herein describedand is limited only by the scope of the invention as defined by theclaims in this specification.

1. A stemming plug which is made from a suitable resiliently deformableplastic material, characterised in that the plug comprises twocup-shaped members which face each other with their rim faces inabutment, a plurality of circumferentially spaced and releasably engagedsocket and spigot formations in arid projecting from the abutting cuprim faces and means, which extends between the centres of the baseportions of the cups in the plug, which is adapted to move the bases ofthe cups towards each other to compress the cups and cause acircumferential zone of the plug on either side of the abutting faces ofthe cups to increase in radial dimension to be brought into load bearingcontact with the side of a predrilled hole in which the plug is to belocated, in use, and to enable the bases of the cups to be moved awayfrom each other to allow the plug to be withdrawn from the hole in theevent of a misfire of an explosive in the hole.
 2. A stemming plug asclaimed in claim 1 wherein a portion of the wall of each cup shapedmember from its rim is substantially cylindrical around the axis of theplug which passes through the centres of the cup bases to define thecircumferential load bearing zone of the plug.
 3. A stemming plug asclaimed in claim 2 wherein each cup-shaped member includes asubstantially cylindrical skirt which extends from the substantiallycylindrical portion of its wall away from the abutting rims of the cupsto surround at least a portion of the cup wall.
 4. A stemming plug asclaimed in claim 3 wherein the composite substantially cylindrical outerwall of the plug is divided into segments by slots which are parallel tothe plug axis.
 5. A stemming plug as claimed in claim 4 wherein theabutting rim faces of each of the wall segments are connected to eachother by the socket and spigot formations.
 6. A stemming plug as claimedin claim 5 wherein the outer surface of each of the wall segmentsinclude outwardly projecting formations for gripping the surface of ahole when the segments are brought into load bearing contact with thesurface, in use.
 7. A stemming plug as claimed in claim 6 wherein thegripping formations are ribs which are parallel to the segment definingslots.
 8. A stemming plug as claimed in claim 4 wherein thenon-cylindrical wall material of each cup-shaped member includes a lineof weakness on the inside of and against the wall of the cup across eachof the wall segment slots.
 9. A stemming plug as claimed in claim 8wherein the line of weakness is defined by arcuate slots with the endsof each slot being spaced from the ends of adjacent slots.
 10. Astemming plug as claimed in claim 9 wherein the non-cylindrical portionof each of the cup-shaped members includes a pleat which extends fromthe ends of each of the arcuate slots in a direction towards the plugaxis to expedite expansion of the plug in a radial direction, in use.11. A stemming plug as claimed in claim 10 wherein the pleated wallmaterial of each cup-shaped member is thinner than the adjacent cup wallmaterial.
 12. A stemming plug as claimed in either one of claim 10wherein the pleats are V-shaped in cross-section,
 13. A stemming plug asclaimed in either one of claim 10 wherein the pleats are C-shaped incross-section.
 14. A stemming plug as claimed in claim 5 wherein thenon-cylindrical portion of each of the cup-shaped members includes anaperture through which a fuse or electrical detonator conductors may bepassed.
 15. A stemming plug as claimed in claim 13 wherein the socketsand spigots on the rim faces of each of the cup-shaped members are soarranged that the fuse apertures in each cup-shaped member are inregister with each other and to prevent rotation of the cups relativelyto each other about the plug axis.
 16. A stemming plug as claimed inclaim 1 wherein a first of the cup-shaped members includes a holed bossin its base and the second an aperture in its base and the cup basemoving means is a headed elongated element which passes axially throughthe plug cavity between the first and second cups with its head, whichis adapted for rotation by a removable toot, bearing on the outersurface of the second cup around the aperture with a portion of itslength from its unheaded end including formations which are movablyengageable with complementally shaped formations in the hole in the bossof the first cup member.
 17. A stemming plug as claimed in claim 16wherein the engageable formations on the end portion of the elongatedelement and in the boss hole are helical thread formations.
 18. Astemming plug as claimed in claim 1 wherein, a first of the cup-shapedmembers includes an aperture in its base around the plug axis, at leasttwo outwardly projecting gripper formations which are attached to andproject outwardly from the base of the cup to be biased towards the plugaxis over the aperture and carry on their faces which face the plug axisratchet teeth, the second cup-shaped member carries an elongated elementwhich passes through the aperture in the first cup and between thegripper formations and carries ratchet teeth which are oppositelydirected to those on the faces of the gripper formations with thedirections of the ratchet teeth being such that the end of the elongatedelement may be pulled outwardly from between the teeth of the gripperformations to draw the cup bases towards each other to set the plug, inuse, when the pulling tension on the elongated element is relaxed.
 19. Astemming plug as claimed in claim 18 including two gripper formationswhich face each other from opposite sides of the aperture in the base ofthe cup and the portion of the elongated element which carries itsratchet teeth is square or rectangular in cross-section with the ratchetteeth on two opposite sides of the element while the remaining oppositesides are flat so that the ratchet teeth on the gripper formations will,when the elongated element and the cup to which it is attached isrotated through 90°, be disengaged from the ratchet teeth on theelongated element to enable the base portions of the cup-shaped elementsof the plug to move away from each other to reduce the radial dimensionof the plug to enable it to be removed from a predrilled hole in theevent of a misfire of the explosive in the hole.
 20. A stemming plug asclaimed in either claim 18 wherein each of the gripper formationsincludes at its free arid a surface which tapers from the end of theformation inwardly towards the plug axis for releasing its ratchet teethfrom those on the elongated element by means of a suitable tool.